What is a travel day?
A travel day is a 24 hour period within which you can travel on trains with your Eurail Pass. It lasts from 12:00 a.m. (midnight) to 11:59 p.m. on the same calendar day. On each travel day, you have access to the train networks where your Eurail Pass is valid.
How does this work with night trains?
When traveling on a night train, you only need to use a single travel day: your day of departure. Even though most night trains leave on one calendar day and arrive on the next, you're never required to use two travel days.
Let us give you an example...
Say that your night train departs on a Monday at 20:00 and arrives at its destination on Tuesday at 10:00. You will only need to use the Monday -your day of departure- as a travel day. If you plan to take more trains on Tuesday -your day of arrival-, you'll have to spend another travel day.